Historical routes to resorcinol-formaldehyde aerogels yield hydrogels which must be supercritically dried in order to retain their nano-porous properties. Even after supercritical drying, exposure to liquids will cause catastrophic failure of the material. Several routes to air-dried aerogels have been published to yield material that can be processed and dried at atmospheric pressure, but have the same catastrophic failure as the supercritically dried aerogel when exposed to liquids.
Phenol formaldehyde polymers have been studied for over 100 years. Acid catalyzed polymers with excess phenol are called Novolacs and base catalyzed polymers with excess formaldehyde are called Resoles. Resorcinol-formaldehyde aerogels were invented in the 1990s. The most common catalyst is sodium carbonate (a base).
Paul Shu (U.S. Pat. No. 4,903,766 (1990)) uses aluminum acetate as a crosslinker for resorcinol and formaldehyde to form a gel that is used to seal pores in oil wells. This application is an in-situ gel formation that forms selectively in the porous structure around the oil well, but it does not forma n aerogel.
Accordingly, there is a need for aerogels that do not experience catastrophic failure when exposed to liquids. Disclosed herein are such aerogels and methods related thereto.